This invention relates to a water purification system and method for purifying raw water such as tap water and groundwater to provide drinking water for domestic or business use.
In a water purification system of the type, sterilization of raw water is carried out in various manners. As a recent technical trend, use has widely been made of a hollow fiber membrane module (commercially available) for destroying microorganisms and bacteria and suppressing growth or propagation thereof. Use is also made of a unit for carrying out electrolysis of the raw water and/or another unit for generating an appropriate amount of chlorine.
Generally, the raw water such as tap water and groundwater contains various pollutants, namely, residual chlorine such as hypochlorous acid (HClO.sup.-), musty odor, trihalomethane, chlorinated organic compounds, pigments, and so on. In the water purification system as a water treatment system, the raw water is made to pass through an adsorber portion (typically, activated carbon) to adsorb and remove the above-mentioned pollutants as adsorbed substances. Thus, the raw water is purified through the adsorber portion to be supplied as purified water. This mode of operation will be referred to as a purification mode throughout the present specification.
In the purification mode, the purified water is supplied in response to a water supply request signal which is produced when a tap is opened. While the supply of the purified water is stopped in absence of the water supply request signal, various kinds of the microorganisms and the bacteria may be grown in the adsorber portion because the flow of the raw water is interrupted. In order to suppress such growth of the microorganisms and the bacteria, the purification mode includes a bacteriostatic operation of applying a weak d.c. voltage to the adsorber portion.
With the lapse of time, the adsorber portion will suffer an accumulation of the adsorbed substances and the growth of the microorganisms and the bacteria. In order to remove the adsorbed substances as well as the microorganisms and the bacteria, the purification mode is followed by a reproduction mode in which the adsorber portion is applied with an a.c. voltage to desorb the adsorbed substances and to destroy and desorb the microorganisms and the bacteria.
In the conventional water purification system described above, tap water typically used as the raw water is made to pass through the adsorber portion to be purified. However, simultaneously when the tap water is purified in the adsorber portion, an effective chlorine component contained in the tap water is also removed. This results in easy growth of the microorganisms and the bacteria in a pipe downstream of the water purification system. In this event, the microorganisms and the bacteria may be mixed into the purified water supplied from the water purification system.
In order to avoid the above-mentioned problem, a chlorine generator is arranged downstream of the water purification system. The chlorine generator is for producing chlorine to compensate the effective chlorine component removed by the adsorber portion.
However, use of the chlorine generator in addition to the water purification system not only requires an additional space for installation thereof but also an additional cost.